Swapping from bottle to cylinder

[woogie_man]

Hey guys,

Say I am playing around with the idea of making a handy little hunting rifle.  Not looking for anything high powered and really wouldn't need a ton of shots.   So looking at ditching the large bottle on one of the rifles and swapping it with a cylinder.  I have been searching and haven't been able to find any sources for a cylinder.

Does anyone know where to find a cylinder, or heck even a small bottle.